Dental suction units, as described for example in WO-A-86/03669, are plagued with special problems because of the composition of the mixture to be suctioned and treated (blood, saliva, water, pus, tooth material, residues of amalgam, etc.), which can lead to serious functional breakdowns. These problems come from cleaning and disinfecting the part of the system through which the mixture flows, which is hereafter called the initial suction line, and also from the fact that blood mixing with the hydrogen peroxide constantly used in dentistry can cause an intensive build-up of foam, which shuts down the system, since the outlet to the vacuum from the trap must naturally be safeguarded against foreign matter flowing through it. The foam that is created has a particularly great stability, and dissolving it automatically takes several hours. On the other hand, dissolving, cleaning and sterilizing a trap is not only time-consuming, but is also an unhygienic activity, since the mixture has a very high concentration of bacteria.
We know how to simplify at least the cleaning or disinfection from EP-B-23036. In it, the outflow duct for the trapped, unseparated mixture of liquids and solid matter has a siphon that siphons off a cleaner from a cleaner container with a rinsing duct at the end whose other end can be connected to a suction hose. The unit can be cleaned or disinfected at the end of a working period, usually at the end of the daily office hours, by connecting the suction hose to the rinsing duct and hooking up the suction unit so that the additive to be added then flows through the initial suction line.
While work is going on, it is hardly possible to add the additive since the equipment makes it impossible for the dentist to work in the interim. According to EP-A-237708, on the other hand, the trap, which has an extraction pump for the trapped liquid and preferably also a centrifuge, is fitted with a propeller, which is between the air trap and the liquid collection space. The foam that builds up is supposed to be destroyed using the propeller. This may work satisfactorily when the pump is running, but when the pump is turned off, the propeller does not prevent the undisturbed, built-up foam from passing through. (The foam build-up takes place gradually, even when the unit is temporarily stopped.) On the other hand, the foam that has gotten into the air trap prevents the suction unit from being turned on, which causes the breakdown mentioned at the beginning. Adding a cleaner or disinfectant is not described in that publication.